1. Field of the Invention
The present invention relates generally to semiconductor devices and manufacturing methods thereof, and more particularly, to a semiconductor device including a plurality of field effect transistors and a manufacturing method thereof.
2. Description of the Background Art
In recent years, as semiconductor devices came to be more densely integrated and reduced in size, 2-power supply devices having external voltage of a conventional level and internal voltage of a lower level have been proposed.
FIG. 79 is a cross sectional view showing such a conventional 2-power supply semiconductor device including a plurality of field effect transistors.
Referring to FIG. 79, the conventional 2-power supply semiconductor device include a first field effect transistor supplied with first power supply voltage (low Vdd) and a second field effect transistor supplied with second power supply voltage (high Vdd) higher than low Vdd formed on a main surface of a p type semiconductor substrate 101 and spaced apart from each other. An isolation oxide film 102 is formed between the first and second field effect transistors.
In the low Vdd region, a pair of first source/drain regions 110 and a pair of low concentration impurity diffusion regions 108 are formed spaced apart from each other on the main surface of semiconductor substrate 101 having a first channel region therebetween. Low concentration, n type impurity diffusion region 108 formed adjacent to the first channel region and high concentration, n type impurity diffusion region 110 formed adjacent to n type impurity diffusion region 108 constitute an LDD (Lightly Doped Drain) structure. A first gate insulating film 106 is formed on the first channel region. A first gate electrode 118 is formed on first gate insulating film 106. A sidewall oxide film 109 is formed on a side of first gate electrode 118. The first field effect transistor supplied with low Vdd is formed of first source/drain regions 110, impurity diffusion regions 108, first gate insulating film 106, and first gate electrode 118.
In the high Vdd region, a pair of second source/drain regions 117 and a pair of low concentration impurity diffusion regions 116 are formed on the main surface of semiconductor substrate 101, spaced apart from each other and having a second channel region therebetween. Second source/drain region 117 and low concentration impurity diffusion region 116, in other words low concentration n type impurity diffusion region 116 formed adjacent to the second channel region and high concentration, n type impurity diffusion region 117 formed adjacent to n type impurity diffusion region 116 constitute an LDD structure. A second gate insulating film 104 is formed on the second channel region. First gate insulating film 106 is formed on second gate insulating film 104. A second gate electrode 119 is formed on first gate insulating film 106. A sidewall oxide film 120 is formed on a side of second gate electrode 119. Second source/drain regions 117 and impurity diffusion region 116, second gate insulating film 104, first gate insulating film 106 and first gate electrode 119 form the second field effect transistor supplied with high Vdd. The gate insulating films 104 and 106 of the second field effect transistor supplied with high Vdd should be thicker than the first gate insulating film 106 of first field effect transistor supplied with low Vdd.
Referring to FIGS. 80 to 86, a method of manufacturing the conventional 2-power supply semiconductor device will be now described.
Isolation oxide film 102 is formed on the main surface of semiconductor substrate 101 to surround an active region. Second gate insulating film 104 is formed on the active region on the main surface of semiconductor substrate 101. A resist pattern 105a is formed on second gate insulating film 104 positioned in the high Vdd region and on isolation oxide film 102. The structure as shown in FIG. 80 is thus obtained.
An isotropic etching is performed using resist pattern 105a as a mask to remove second gate insulating film 104 positioned in the low Vdd region to obtain the structure as shown in FIG. 81. Resist pattern 105a is then removed.
As shown in FIG. 82, first gate insulating film 106 is formed on the main surface of semiconductor substrate 101 and on second gate insulating film 104.
A first doped polysilicon film 103 (see FIG. 83) is deposited on first gate insulating film 106 and isolation oxide film 102. Resist patterns 105b and 105c are formed on the regions of first doped polysilicon film 103 to be first and second gate electrodes 118 and 119 (see FIG. 79). The structure as shown in FIG. 83 is thus obtained.
Then, using resist patterns 105b and 105c as masks, an anisotropic etching is performed to remove a part of first doped polysilicon film 103, and first and second gate electrodes 118 and 119 are formed as a result. Resist patterns 105b and 105c are then removed. The structure as shown in FIG. 84 is thus obtained. The gate insulating film portion of the second field effect transistor formed of first and second gate insulating films 106 and 104 can be made thicker than the first gate insulating film 106 of the first field effect transistor. Thus, the breakdown voltage of the second field effect transistor can be greater than the breakdown voltage of the first field effect transistor, so that the second field effect transistor may be supplied with voltage higher than the first field effect transistor.
As shown in FIG. 85, an n type impurity is introduced into a prescribed region of the main surface of semiconductor substrate 101 to form low concentration n type impurity diffusion regions 108 and 116.
Sidewall oxide films 109 and 120 (see FIG. 86) are formed on sides of first and second gate electrodes 118 and 119. An n type impurity is then introduced into a prescribed region of the main surface of semiconductor substrate 101 to form high concentration n type impurity diffusion regions 110 and 117 as shown in FIG. 86.
The conventional 2-power supply semiconductor device is manufactured as described above.
In the manufacture of the 2-power supply semiconductor device, resist pattern 105a is directly formed on second gate insulating film 104 positioned in the high Vdd region. In the following removal of resist pattern 105a, defects (local irregularities) are sometimes generated in the surface of second gate insulating film 104. A light etching processing for removing resist pattern 105a is directly performed to the surface of second gate insulating film 104, second gate insulating film 104 may be reduced in thickness. The defects in the surface of second gate insulating film 104 and the reduction in thickness lead to a reduction in the breakdown voltage of second gate insulating film 104, and as a result electrical characteristics of the semiconductor device including the field effect transistor deteriorate.
As a countermeasure, a manufacturing method as shown in FIGS. 87 to 93 has been proposed.
Referring to FIGS. 87 to 93, the proposed conventional method of manufacturing a 2-power supply semiconductor device including a plurality of field effect transistors will be described.
Isolation oxide film 102 is formed on the main surface of p type semiconductor substrate 101 to surround an active region. Second gate insulating film 104 is formed on the active region in the main surface of p type semiconductor substrate 101. First doped polysilicon film 103 is formed on second gate insulating film 104 and isolation oxide film 102. Resist pattern 105a is formed on the region of first doped polysilicon film 103 to be second gate electrode 119 (see FIG. 88) positioned in the high Vdd region to obtain the structure as shown in FIG. 87.
An anisotropic etching is performed using resist pattern 105a as a mask to etch away a part of first doped polysilicon film 103, and second gate electrode 119 as shown in FIG. 88 results. Resist pattern 105a is then removed. Resist pattern 105b is formed on second gate insulating film 104 positioned in the high Vdd region and second gate electrode 119 to form the structure as shown in FIG. 88.
In the manufacture, second gate electrode 119 is formed on second gate insulating film 104 and then resist pattern 105b is formed. Resist pattern 105b is not directly formed on the region of the surface of second gate insulating film 104 in contact with second gate electrode 119. Thus, defects in the surface of second gate insulating film 104 as in the manufacturing method shown in FIGS. 80 to 86 can be prevented.
Then, as shown in FIG. 89, second gate insulating film 104 positioned in the low Vdd region is removed by an isotropic etching. Then, resist pattern 105b is removed.
As shown in FIG. 90, a silicon oxide film to be first gate insulating film 106 is formed on the main surface of p type semiconductor substrate 101 positioned in the low Vdd region and on second gate insulating film 104 and second gate electrode 119.
Then, on first gate insulating film 106 and isolation oxide film 102, a second doped polysilicon film 107 (see FIG. 91) is formed by means of CVD. Resist pattern 105c (see FIG. 91) is formed on the region of second doped polysilicon film 107 to be first gate electrode 118 (see FIG. 93). The structure as shown in FIG. 91 is thus obtained.
An anisotropic etching is performed using resist pattern 105c as a mask to remove a part of second doped polysilicon film 107, and first gate electrode 118 (see FIG. 92) is formed as a result. After the anisotropic etching, a part of second doped polysilicon film 107 also remains on a side of second gate electrode 119. Resist pattern 105c is then removed. Resist pattern 105d (see FIG. 92) is formed on first gate insulating film 106 positioned in the low Vdd region and on first gate electrode 118. Thus, the structure as shown in FIG. 92 results.
Second doped polysilicon film 107 remaining on the side of second gate electrode is removed by an isotropic etching, and then resist pattern 105d is removed. After low concentration, n type impurity diffusion regions 108, 116 (see FIG. 93) are formed by introducing an impurity, sidewall oxide films 109, 120 (see FIG. 93) are formed, followed by formation of high concentration n type impurity diffusion regions 110, 117 (see FIG. 93), and the semiconductor device as shown in FIG. 93 results.
In the manufacture of the proposed conventional 2-power supply semiconductor device as shown in FIGS. 87 to 93, second gate electrode 119 is formed before resist pattern 105b is formed as shown in FIG. 88, in order to prevent defects from being formed in the surface of second gate insulating film 104. In the manufacture of the 2-power supply semiconductor device, however, in the step as shown in FIG. 90, during forming first gate insulating film 106, second gate electrode 119 formed of doped polysilicon is oxidized in an end 123 of the contact portion between second gate electrode 119 and second gate insulating film 104 as shown in FIG. 94. Therefore, a silicon oxide film 124 grows along the contact surface between second gate insulating film 104 and second gate electrode 119. Thus grown silicon oxide film is called xe2x80x9cgate bird""s beakxe2x80x9d. Herein, FIG. 94 is an enlarged view of region 100 shown in FIG. 90. The gate oxide film having a xe2x80x9cgate bird""s beakxe2x80x9d formed of an oxide film is poor in quality and difficult to control in thickness. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors deteriorate.
The present invention is directed to a solution to the above-described problems. It is one object of the invention to provide a semiconductor device which can prevent electrical characteristics of the device from deteriorating by preventing the deterioration of the quality of a gate insulating film.
Another object of the invention is to provide a semiconductor device which can prevent a gate bird""s beak from being generated.
Yet another object of the invention is to provide a method of manufacturing a semiconductor device which can prevent the deterioration of the quality of a gate insulating film.
A semiconductor device according to one aspect of the invention having a plurality of field effect transistors includes first and second field effect transistors.
The first field effect transistor includes a pair of first source/drain regions, a first gate insulating film, and a first gate electrode. The second field effect transistor includes a pair of second source/drain regions, a second gate insulating film, and a second gate electrode. The first source/drain regions are formed, on a main surface of a semiconductor substrate, spaced apart from each other and having a first channel region therebetween. The first gate insulating film is formed on the first channel region in a first thickness. The second source/drain regions are formed on the main surface of the semiconductor substrate, spaced apart from each other and having a second channel region therebetween. The second gate insulating film is formed on the second channel region in a second thickness larger than the first thickness. The second gate electrode is formed on the second gate insulating film. An oxidation protection film to prevent one of the first and second gate electrodes from being oxidized is formed on a side of one of the gate electrodes. In the semiconductor device according to this aspect, the oxidation protection film to prevent the gate electrode from being oxidized is formed on a side of one of the first and second gate electrodes, and therefore an oxidizing step to form a gate insulating film of another field effect transistor may be performed while the oxidization protection film is formed on a side of that one gate electrode. As a result, the lower part of the side of the gate electrode can be prevented from being oxidized, and a gate bird""s beak can be avoided. Thus, the threshold voltages of the field effect transistors can be prevented from increasing. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating.
A semiconductor device according to another aspect of the invention having a plurality of field effect transistors includes first and second field effect transistors.
The first field effect transistor includes a pair of first source/drain regions, a first gate insulating film, and a first gate electrode. The second field effect transistor includes a pair of second source/drain regions, a second gate insulating film, and a second gate electrode. The first source/drain regions are formed, on a main surface of a semiconductor substrate, spaced apart from each other and having a first channel region therebetween. The first gate insulating film has a first thickness and is formed on the first channel region to include an oxide nitride film. The first gate electrode is formed on the first gate insulating film. The second source/drain regions are formed, on the main surface of the semiconductor substrate, spaced apart from each other and having a second channel region therebetween. The second gate insulating film is formed on the second channel region and has a second thickness larger than the first thickness. The second gate electrode is formed on the second gate insulating film.
In the semiconductor device according to this aspect, since the first gate insulating film is formed to include the oxide nitride film, in the manufacturing process which will be described, in the presence of the second gate electrode, during forming the oxide nitride film to be the first gate insulating film, an end of the second gate electrode can be prevented from being excessively oxidized in the contact portion between a lower part of a side of the second gate electrode and the second gate insulating film. Thus, as a result, the lower part of the side of the gate electrode can be prevented from being oxidized, and a gate bird""s beak can be avoided. Thus, the threshold voltages of the field effect transistors can be prevented from increasing. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating. Furthermore, since the first gate insulating film is formed to include the oxide nitride film, the first gate insulating film may be formed thinner with a prescribed breakdown voltage being maintained than the case of using a conventional silicon oxide film or the like. As a result, the driving voltage of the first field effect transistor may be reduced.
A semiconductor device according to another aspect of the invention having a plurality of field effect transistors includes first and second field effect transistors. The first field effect transistor includes a pair of first source/drain regions, a first gate insulating film, and a first gate electrode. The second field effect transistor includes a pair of second source/drain regions, a second gate insulating film, and a second gate electrode. The first source/drain regions are formed, on a main surface of a semiconductor substrate, spaced apart from each other and having a first channel region therebetween. The first gate insulating film is formed on the first channel region and has a first thickness. The first gate electrode is formed on the first gate insulating film. The second source/drain regions are formed, on the main surface of the semiconductor substrate, spaced apart from each other and having a second channel region therebetween. The gate insulating film is formed on the second channel region and has a second thickness larger than the first thickness. The second gate electrode is formed on the second gate insulating film. An anti-oxidation conductive film is formed on at least one of the first and second gate insulating films.
In the semiconductor device according to this aspect, the anti-oxidation conductive film is formed on at least one of the first and second gate insulating films, it is not necessary to form a resist pattern directly on the surface of one of the first and second gate insulating films in the following manufacturing steps. Furthermore, before forming one of the first and second gate electrodes, an oxidizing step to form the other one of the first and second gate insulating films may be performed using the anti oxidation conductive film. Thus, in the step of oxidizing the first gate insulating film, a lower part of the side of one of the first and second gate electrodes can be prevented from being oxidized, and a gate bird""s beak can be avoided. Thus, the threshold voltages of the field effect transistors can be prevented from increasing. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating.
Furthermore, since the anti-oxidation conductive film is formed on one of the first and second gate insulating films, a resist pattern will not be formed directly on one of the first and second gate insulating films in the following manufacturing steps. As a result, defects such as local irregularities in the gate insulating film as formed during removing the resist pattern can be avoided. Therefore, the threshold voltages of the field effect transistors may be prevented from fluctuating. Electrical characteristics of the semiconductor device including the plurality of field effect transistors may be prevented from deteriorating.
In the semiconductor device according to this aspect, a semiconductor film having a conductive impurity may be formed at a position between the anti-oxidation conductive film and at least one of the first and second gate insulating films.
Thus, when voltage is supplied to one of the first and second gate electrodes having the semiconductor film including the conductive impurity, the formation of a depletion layer caused by a reduction in the concentration of the conductive impurity in the vicinity of one of the first and second gate insulating films may be prevented. As a result, the fluctuation of the threshold voltages of the field effect transistors caused by the formation of such a depletion layer can be prevented. Therefore, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating.
A semiconductor device according to another aspect of the invention having a plurality of field effect transistors includes first and second field effect transistors.
The first field effect transistor includes a pair of first source/drain regions, a first gate insulating film, and a first gate electrode. The second field effect transistor includes a pair of second source/drain regions, a second gate insulating film, and a second gate electrode. The first source/drain regions are formed, on a main surface of a semiconductor substrate, spaced apart from each other and having a first channel region therebetween. The first gate insulating film is formed on the first channel region and has a first thickness. The first gate electrode is formed on the first gate insulating film. The second source/drain regions are formed, on the main surface of the semiconductor substrate, spaced apart from each other and having a second channel region therebetween. The second gate insulating film is formed on the second channel region and has a second thickness. The second gate electrode is formed on the second gate insulating film. A semiconductor film having a conductive impurity is formed on and in contact with at least one of the first and second gate insulating films. An anti-oxidation insulating film for preventing the semiconductor film having the conductive impurity from being oxidized is formed on the semiconductor film.
Since the semiconductor film having the conductive impurity is thus formed on and in contact with one of the first and second gate insulating films, it is not necessary to form a resist pattern directly on a surface of one of the first and second gate insulating films in the manufacture of the semiconductor device. Furthermore, before one of the first and second gate electrodes is formed, an oxidizing step to form the other one of the first and second gate insulating films may be performed using the anti-oxidation insulating film as a mask. In the step of oxidizing the gate insulating films, a lower part of a side of the gate electrodes can be prevented from being oxidized as a result, and a gate bird""s beak can be avoided. Thus, the threshold voltages of the field effect transistors can be prevented from increasing. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating.
Furthermore, the semiconductor film having the conductive impurity is formed on and in contact with one of the first and second gate insulating films, a resist pattern is not formed directly on one of the first and second gate insulating films. As a result, defects such as local irregularities in the gate insulating films as formed during removing the resist pattern can be avoided. Therefore, the threshold voltages of the field effect transistors may be prevented from fluctuating. Electrical characteristics of the semiconductor device including the plurality of field effect transistors may be prevented from deteriorating. Furthermore, when voltage is supplied to one of the first and second gate electrodes having the semiconductor film including the conductive impurity, the formation of a depletion layer caused by a reduction in the concentration of the conductive impurity in the vicinity of one of the first and second gate insulating films may be prevented. As a result, the fluctuation of the threshold voltages of the field effect transistors caused by the formation of such a depletion layer can be prevented. Therefore, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating.
A semiconductor device according to another aspect of the invention having a plurality of field effect transistors includes first and second field effect transistors.
The first field effect transistor includes a pair of first source/drain regions, a first gate insulating film, and a first gate electrode. The second field effect transistor includes a pair of second source/drain regions, a second gate insulating film, and a second gate electrode. The second gate electrode has a first conductive film, an insulating film and a second conductive film. The first source/drain regions are formed, on a main surface of a semiconductor substrate, spaced apart from each other and having a first channel region therebetween. The first gate insulating film is formed on the first channel region and has a first thickness. The first gate electrode is formed on the first gate insulating film. The second source/drain regions are formed, on the main surface of the semiconductor substrate, spaced apart from each other and having a second channel region therebetween. The second gate insulating film is formed on the second channel region and has a second thickness. The first conductive film to be a part of the second gate electrode is formed on the second gate insulating film. The insulating film to be a part of the second gate electrode is formed on the first conductive film. The second conductive film to be a part of the second gate electrode is formed on the insulating film.
Thus, the second gate electrode has the first conductive film, the insulating film, and the second conductive film, and therefore an oxidizing step for forming the first gate insulating film can be performed before forming the second gate electrode without forming a resist pattern directly on the surface of the second gate insulating film. As a result, a lower part of a side of the gate electrode can be prevented from being oxidized, and a gate bird""s beak can be avoided. Thus, the threshold voltages of the field effect transistors can be prevented from increasing. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating.
A semiconductor device according to another aspect of the invention having a plurality of field effect transistors includes first and second field effect transistors.
The first field effect transistor includes a pair of first source/drain regions, a first gate insulating film, and a first gate electrode. The second field effect transistor includes a pair of second source/drain regions, a second gate insulating film, and a second gate electrode. The first source/drain regions are formed, on a main surface of a semiconductor substrate, spaced apart from each other and having a first channel region therebetween. The first gate insulating film is formed on the first channel region and has a first thickness. The first gate electrode is formed on the first gate insulating film. The second source/drain regions are formed, on the main surface of the semiconductor substrate, spaced apart from each other and having a second channel region therebetween. The second gate insulating film is formed on the second channel region and has a second thickness larger than the first thickness. The second gate electrode is formed on the second gate insulating film. A protection conductive film is formed on and in contact with at least one of the first and second gate insulating films.
Thus, the protection conductive film is formed on and in contact with one of the first and second gate insulating films, it is not necessary to form a resist pattern directly on the surface of one of the first and second gate insulating films. Furthermore, before forming one of the first and second gate electrodes, an oxidizing step for forming the other one of the first and second gate insulating films can be performed using the protection conductive film. Thus, in the step of oxidizing the gate insulating films, a lower part of a side of one of the first and second gate electrodes can be prevented from being oxidized, and a gate bird""s beak can be avoided. Thus, the threshold voltages of the field effect transistors can be prevented from increasing. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating.
In the semiconductor device according to this aspect, the protection conductive film includes first and second protection conductive films. The first protection conductive film may be formed on and in contact with the first gate insulating film, while the second protection conductive film may be formed on and in contact with the second gate insulating film. The first and second protection conductive films may be substantially equal in thickness.
Thus, during etching the first and second protection conductive films to form the first and second gate electrodes, the part of the thickness of the first and second protection conductive films to be removed by the etching can be made substantially equal in the regions to form the first and second gate electrodes. As a result, during the etching for forming the first and second gate electrodes, the amount of etching for forming the first gate electrode can be substantially the same as the amount of etching for forming the second gate electrode. Therefore, the amount of overetching during forming the first and second gate electrodes can be reduced. As a result, the semiconductor substrate or the like positioned under the protection conductive films to be etched away can be prevented from being damaged by overetching. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating.
The semiconductor device according to this aspect may further include a protection conductive film formed by depositing a film having an amorphous structure. Thus, the film having the amorphous structure is free from grain boundaries, and therefore during isotropically etching the protection conductive film in the manufacture of the semiconductor device, damages to the gate insulating film positioned under the protection conductive film caused by the isotropic etching agent running along grain boundaries can be prevented. As a result, the fluctuation of the threshold voltages of the field effect transistors can be prevented. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented.
In the semiconductor device according to this aspect, an anti-oxidation film may be formed on and in contact with the protection conductive film. Thus, in the manufacture of the semiconductor device, a natural oxide film difficult to control in thickness can be prevented from being formed on the protection conductive film. Thus, in an etching step to form the first and second gate electrodes, the variation of the thickness of the protection conductive film to be etched away caused by the formation of such a natural oxide film can be prevented. As a result, during etching for forming the first and second gate electrodes, the variation of the thickness of the protection conductive film to be etched away can be reduced, the amount of overetching, can be reduced. As a result, damages to the semiconductor substrate or the like positioned under the protection conductive film to be etched away, caused by overetching can be prevented.
In a method of manufacturing a semiconductor device according to another aspect of the invention, a first gate insulating film having a first thickness is formed on a main surface of a semiconductor device. A first gate electrode is formed on the first gate insulating film. Using the gate electrode as a mask, an impurity is introduced into the main surface of the substrate to form a pair of first source/drain regions, spaced apart from each other and having a first channel region therebetween. A second gate insulating film having a second thickness larger than the first thickness is formed on the main surface of the semiconductor substrate. Using the second gate electrode as a mask, an impurity is introduced into the main surface of the substrate to form a second pair of source/drain regions, spaced apart from each other and having a second channel region therebetween. An oxidation protection film to prevent a gate electrode from being oxidized is formed on a side of one of the first and second gate electrodes. After one of the first and second gate insulating films is formed, the other one of the first and second gate insulating films is formed with the oxidation protection film being present on the side of the gate electrode formed on that one of the first and second gate insulating films.
Thus, with the gate electrode being formed on one of the first and second gate insulating films, the other one of the first and second gate insulating films is formed, and therefore resist pattern is not directly formed on the gate insulating film. Therefore, during the following removal of the resist pattern, a direct light etching processing can be prevented on the surface of the gate insulating film. As a result, defects in the surface of the gate insulating film caused by such a light etching processing can be prevented. Furthermore, with the oxidation protection film for preventing a gate electrode from being oxidized being present on a side of one of the first and second gate electrodes, an oxidizing step to form the other one of the first and second gate insulating films is performed. As a result, a lower part of a side of the gate electrode can be prevented from being oxidized, and a gate bird""s beak can be avoided. Thus, the threshold voltages of the field effect transistors can be prevented from increasing. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating.
In a method of manufacturing a semiconductor device according to another aspect of the invention, a first gate insulating film including an oxide nitride film and having a first thickness is formed on a main surface of a semiconductor substrate. A first gate electrode is formed on the first gate insulating film. Using the gate electrode as a mask, an impurity is introduced into the main surface of the substrate to form a pair of first source/drain regions, spaced apart from each other and having a first channel region therebetween. A second gate insulating film having a second thickness larger than the first thickness is formed on the main surface of the semiconductor substrate. Using the second gate electrode as a mask, an impurity is introduced into the main surface of the substrate to form a second pair of source/drain regions, spaced apart from each other and having a second channel region therebetween. The first gate insulating film is formed in the presence of the second gate electrode formed on the second gate insulating film.
Thus, while the second gate electrode has been formed on the second gate insulating film, the first gate insulating film is formed, and therefore resist pattern is not directly formed on the second gate insulating film. Therefore, during the following removal of the resist pattern, a direct light etching processing on the surface of the second gate insulating films can be prevented. Thus, defects in the surface of the second gate insulating film caused by such a light etching processing can be prevented.
Furthermore, since there is the step of forming the first gate insulating film to include the oxide nitride film, an end of the second gate electrode can be suppressed from being excessively oxidized at the joint of a lower part of a side of the second gate electrode and the second gate insulating film during forming the oxide nitride film to be the first gate insulating film while the second gate electrode has been formed. Thus, a gate bird""s beak can be avoided. Therefore, the threshold voltages of the field effect transistors can be prevented increasing, and as a result electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating. Since the first gate insulating film is formed to include the oxide nitride film, the thickness of the first gate insulating film can be made smaller than the case of using a conventional silicon oxide film as a prescribed breakdown voltage is maintained. As a result, the driving voltage of the first field effect transistor can be reduced.
In a method of manufacturing a semiconductor device according to another aspect of the invention, a first gate insulating film having a first thickness is formed on a main surface of a semiconductor substrate. A first gate electrode is formed on the first gate insulating film. Using the first gate electrode as a mask, an impurity is introduced into the main surface of the substrate to form a pair of first source/drain regions, spaced apart from each other and having a first channel region therebetween. A second gate insulating film having a second thickness larger than the first thickness is formed on the main surface of the semiconductor substrate. Using the second gate electrode as a mask, an impurity is introduced into the main surface of the substrate to form a second pair of source/drain regions, spaced apart from each other and having a second channel region therebetween. An anti-oxidation conductive film is formed on at least one of the first and second gate insulating films. While the anti-oxidation conductive film has been formed on at least one of the first and second gate insulating films, the other one of the first and second gate insulating films is formed.
Since the anti-oxidation conductive film is formed on one of the first and second gate insulating films, it is not necessary to directly form a resist pattern on the surface of one of the first and second gate insulating films. In addition, before forming one of the first and second gate electrodes, an oxidizing step to form the other one of the first and second gate insulating films can be performed using the anti-oxidation conductive film as a mask. As a result, a lower part of a side of one of the first and second gate electrodes can be prevented from being oxidized, and a gate bird""s beak can be avoided. Thus, the threshold voltages of the field effect transistors can be prevented from increasing. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating.
Furthermore, since the anti-oxidation conductive film is formed on one of the first and second gate insulating films, a resist pattern is not directly formed on that one of the first and second gate insulating films. As a result, defects such as local irregularities in the gate insulating film as formed during removing a resist pattern can be avoided. Therefore, the threshold voltages of the field effect transistors may be prevented from fluctuating. Electrical characteristics of the semiconductor device including the plurality of field effect transistors may be prevented from deteriorating.
The method of manufacturing the semiconductor device according to this aspect may further include the step of forming a semiconductor film including a conductive impurity at a position between the anti-oxidation conductive film and at least one of the first and second gate insulating films. Thus, when voltage is supplied to one of the first and second gate electrodes on the side having the semiconductor film including the conductive impurity, the formation of a depletion layer caused by a reduction in the concentration of the conductive impurity in the vicinity of one of the first and second gate insulating films can be restricted. As a result, the fluctuation of the threshold voltages of the field effect transistors caused by the formation of such a depletion layer can be prevented. Therefore, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating.
In the method of manufacturing the semiconductor device according to this aspect, a substrate protection film may be formed in the region on the main surface of the semiconductor substrate to form one of the first and second gate insulating films. With the substrate protection film being present, the other one of the first and second gate insulating films and the anti-oxidation conductive film may be formed.
Thus, with the presence of the substrate protection film, the other one of the first and second gate insulating films and the anti-oxidation conductive film are formed, the insulating film forming the other one of the first and second gate insulating film can be prevented from being formed in contact with the main surface of the semiconductor substrate positioned in the region to form one of the first and second gate insulating films.
As a result, during etching away the anti-oxidation conductive film and the insulating film from the region to form one of the first and second gate insulating films, the main surface of the semiconductor substrate positioned in the region to form that one of the first and second gate insulating films can be prevented from being directly etched. Thus, damages to the main surface of the semiconductor substrate caused by etching can be prevented. As a result, during forming one of the first and second gate insulating films, the deterioration of the quality of one of the first and second gate insulating films caused by the presence of damages by the etching on the main surface of the semiconductor substrate in which the gate insulating film is formed can be prevented. As a result, the fluctuation of the threshold voltage of the field effect transistors can be prevented. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented.
The method of manufacturing the semiconductor device according to this aspect may further include the step of removing a part of the main surface of the semiconductor substrate positioned in the region to form one of the first and second gate insulating films before forming that insulating film.
Thus, in the main surface of the semiconductor substrate positioned in the region to form one of the first and second gate insulating films by means of etching in the manufacture of the semiconductor device, a part of the main surface of the semiconductor substrate with damages such as local irregularities can be removed. Therefore, that one of the first and second gate insulating films can be formed on the main surface of the semiconductor substrate removed of the damaged part. Therefore, the quality of the gate insulating film can be prevented from deteriorating due to damages on the main surface of the semiconductor substrate. The fluctuation of the threshold voltages of the field effect transistors can be prevented. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented.
In a method of manufacturing a semiconductor device according to another aspect of the invention, a first gate insulating film having a first thickness is formed on a main surface of a semiconductor device. A first gate electrode is formed on the first gate insulating film. Using the gate electrode as a mask, an impurity is introduced into the main surface of the substrate to form a pair of first source/drain regions, spaced apart from each other and having a first channel region therebetween. A second gate insulating film having a second thickness larger than the first thickness is formed on the main surface of the semiconductor substrate. A first conductive film to be a part of a second electrode is formed on the second gate insulating film. An insulating film to be a part of the second gate electrode is formed on the first conductive film. A second conductive film to be a part of the second gate electrode is formed on the insulating film. The first and second insulating films and the insulating film are anisotropically etched to form the second gate electrode. Using the second gate electrode as a mask, an impurity is introduced into the main surface of the substrate to form a second pair of source/drain regions, spaced apart from each other and having a second channel region therebetween. Herein the first gate insulating film is formed in the presence of the first conductive film.
Thus, after forming the first conductive film to be a part of the second gate electrode on the second gate insulating film, the first gate insulating film is formed, and therefore an oxidizing step to form the first gate insulating film can be performed without forming a resist pattern directly on the surface of the second gate insulating film. Therefore, during the following removal of the resist pattern, a direct light etching processing to the surface of the second gate insulating film can be prevented. Thus, defects on the surface of the second gate insulating film caused by such a light etching processing can be prevented.
In the presence of the first conductive film, after the first gate insulating film is formed and then the insulating film and the second conductive films are formed, the first and second conductive films and the insulating film are anisotropically etched to form the second gate electrode, a side of the second gate electrode can be prevented from being oxidized in the oxidizing step to form the first gate insulating film. Thus, a gate bird""s beak can be avoided. Thus, the threshold voltages of the field effect transistors can be prevented from increasing. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating. In the presence of the insulating film, when a voltage is supplied to the second gate electrode, the voltage drops in the insulating film, and voltage imposed on the second gate insulating film can be reduced.
In a method of manufacturing a semiconductor device according to another aspect of the invention, a first gate insulating film having a first thickness is formed on a main surface of a semiconductor substrate. A first gate electrode is formed on the first gate insulating film. Using the gate electrode as a mask, an impurity is introduced into the main surface of the substrate to form a pair of first source/drain regions, spaced apart from each other and having a first channel region therebetween. A second gate insulating film having a second thickness larger than the first thickness is formed on the main surface of the semiconductor substrate. A second gate electrode is formed on the second gate insulating film. Using the second gate electrode as a mask, an impurity is introduced into the main surface of the substrate to form a pair of second source/drain regions, spaced apart from each other and having a second channel region therebetween. A protection conductive film for protecting a gate insulating film is formed on and in contact with at least one of the first and second gate insulating films. While the protection conductive film has been formed, the other one of the first and second gate insulating films is formed.
Thus, the protection conductive film is formed on and in contact with one of the first and second gate insulating films, it is not necessary to directly form a resist pattern on that one of the first and second gate insulating films. Furthermore, before forming one of the first and second gate electrodes, an oxidizing step to form the other one of the first and second gate insulating films using the protection conductive film as a mask can be performed. As a result, a lower part of the side of one of the first and second gate electrodes can be prevented from being oxidized, and a gate bird""s beak can be avoided. Thus, the threshold voltages of the field effect transistors can be prevented from increasing. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating.
In the method of manufacturing the semiconductor device according to this aspect, a conductive film may be formed on and in contact with the other one of the first and second gate insulating films. A resist pattern may be formed on and in contact with the conductive film and the protection conductive film. Using the resist pattern as a mask, part of the conductive film and the protection conductive film is anisotropically etched away to simultaneously form the first gate electrode and the second gate electrode.
Thus, the resist pattern is formed on and in contact with the protection conductive film and the conductive film, part of the conductive film and the protection conductive film is anisotropically etched away using the resist pattern as a mask, and therefore the first and second gate electrodes can be formed only of the conductive film and the protection conductive film. As a result, it is not necessary to further form a conductive film to be a part of the gate electrode on the protection conductive film, the process of manufacturing the semiconductor device can be simplified.
In a method of manufacturing a semiconductor device according to another aspect of the invention, an insulating film is formed on a main surface of a semiconductor substrate positioned in regions to form first and second field effect transistors. A resist pattern is formed on the insulating film positioned in the regions to form the second field effect transistor. Using the resist pattern as a mask, a part of the insulating film positioned in the region to form the first field effect transistor is isotropically etched away, followed by removal of the resist pattern. Thus a part of the surface of the insulating film is isotropically etched away to form first and second gate insulating films. A first gate electrode is formed on the first gate insulating film. Using the first gate electrode as a mask, an impurity is introduced into the main surface of the semiconductor substrate to form a pair of source/drain regions, spaced apart from each other and having a first channel region therebetween. A second gate electrode is formed on the second gate insulating film. Using the second gate electrode as a mask, an impurity is introduced into the main surface of the semiconductor substrate, to form a pair of second source/drain regions, spaced apart from each other and having a second channel region therebetween.
Thus, the first and second gate insulating films are formed of a single insulating film, only a single oxidizing step is necessary to form the first and second gate insulating films. Since the first and second gate electrodes are formed after forming the first and second gate insulating films, thus first and second gate electrodes are not oxidized during forming the first and second gate insulating films. As a result, a lower part of a side of the first and second gate electrodes can be prevented from being oxidized, and a gate bird""s beak can be avoided. Thus, the threshold voltages of the field effect transistors can be prevented from increasing. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating.
Furthermore, since only a single oxidizing step is necessary to form the first and second gate insulating films, in other words the number of oxidizing steps to form insulating films is reduced by one as compared to the conventional method, the process of manufacturing the semiconductor device can be simplified.
Furthermore, the first and second gate insulating films are formed by means of isotropic etching, possible defects such as local irregularities caused by for example a step of ashing during removal of the resist pattern on the insulating film to be the first and second gate insulating films can be removed by the anisotropic etching. As a result, a defectless, highly reliable gate insulating film may be obtained, and the fluctuation of the threshold voltages of the field effect transistors can be prevented. As a result, electrical characteristics of the semiconductor device including the plurality of field effect transistors can be prevented from deteriorating.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.